Glutathione (GSH) is a major antioxidant present in high concentrations in nearly all living cells, with numerous critical functions in cellular homeostasis and defense. The investigator's previous results and those of others suggest that GSH depletion is a general phenomenon of aging tissues and organisms. They hypothesize that the loss of GSH is caused by an impairment in its biosynthesis and represents a key factor in the biological aging process, based upon its essential roles. While considerable data have been accumulated to support the important role for GSH in aging, little information is available regarding the mechanisms responsible for its depletion during aging. The overall goals of the present research proposal are to determine the cause of the GSH deficiency in the aging mouse and to elucidate the mechanisms by which caloric restriction (CR) increases GSH and prevents the aging-deficiency. To this end, they will determine the effects of aging and CR on the metabolism of Met, Cys and GSH in the C57BL/6 mouse model. In addition, they will also examine the effects of specific enhancement and depletion of GSH on longevity, using lifelong feeding with GSH monoethyl ester and buthionine sulfoximine, respectively. A systematic and multi-level approach will be used to assess metabolism. The specific activities of the enzymes involved in GSH, Cys and Met metabolism will be determined along with the levels of specific intermediate metabolites in different tissues. GSH turnover will be assessed on whole animals by injection of radiolabeled precursors. Animals of 4 age groups will be analyzed in order to assess growth and developmental changes as well as aging-specific changes. The results of these studies will provide new information on the biochemical mechanisms of the aging process, which will be important in the development of strategies to enhance health and longevity.